Iodine, in the form of Lugol's solution or tincture of iodine, has long been recognized as an effective biocide. Compounded iodine in the form of an iodophor has also been noted for these biocidal properties since 1960. Biocide properties of iodine have been documented since at least as early as 1830.
Iodine is an essential element in the body for bio-activity in humans, animals and birds, aquatic animals and fish, and in plant life. For example, iodine is essential for the function of the thyroid in human beings (The Pharmacological Basis for Therapeutics, 5th edition, L. S. Goodman and A. Gilman, Chapter 67, “Thyroid and Anti-thyroid drugs”) and necessitates an adequate daily intake of iodine, typically 150 micrograms for an adult. Without normal amounts of iodine, the thyroid-stimulating hormone (TSH or thyrotropin) no longer properly stimulates and controls the thyroid-releasing hormone thyroxine. Thyroxine, an amino acid of the thyroid gland, contains iodine. If the thyroxine is excreted in excess, the thyroid hypertrophies and the body's metabolism is stimulated in an undesirable manner. This condition, hyperthyroidism, manifests itself in over-activity of the thyroid gland. Another consequence of iodine deficiency in the diet is the possible contraction of hypothyroidism, i.e. underactivity of the thyroid gland, which results in slowing down the body's metabolism and causing goitre and mental deficiencies.
Many parts of the world, especially former glaciated areas, are deficient in dietary iodine. The richest sources of dietary iodine are those derived from marine life. Seafish contain 200 to 1000 micrograms/kg and shellfish a similar amount. To obtain the recommended level of 150 microgram daily, a standard adult human requirement, one would have to eat 5 kg of vegetables or 3 kg of meat or freshwater fish. To promote iodine sufficiency, iodine is provided as a dietary supplement in many countries by addition of iodate to table salt, typically at a level of 100 micrograms/gram of salt.
A major potential use of aqueous iodine solutions is in disinfection, sterilization and preservation of food stuffs and feed stuffs. There is a growing concern about bacterial, viral and protozoal contamination of ingredients for human foods and finished human food products. Bacteria of major concern include Salmonella, Typhinium, Staphylococcus Aureus, Vibrio Cholera, Bacillus Anthracis and certain strains of E. Coli. Examples of viruses are poliomyelitis and influenza. Examples of protozoa are Giardia, Chlamydomonas and Entamoeba. 
While the disinfecting, sterilizing and preserving properties of dilute aqueous iodine solutions have been known for at least a century, the use with food ingredients, food stuffs, feed ingredients and feeds has been very limited apart from the notable case of iodized salt consumption by humans and animals. The reasons for the lack of application have been several fold:                a) It was believed that high concentrations (30 mg/L or higher) were needed to be effective. At these levels there is distinct coloration of the solution and a strong iodine taste when added to products.        b) It was difficult to prepare dilute aqueous iodine solutions in a controllable manner in an industrial environment. A further impediment was that the techniques used often resulted in solutions contaminated with solid iodine or iodine compounds which were considered a health risk.        
A number of patents and other publications have recorded different approaches to producing solutions of iodine in water. These range from the classical iodine saturator as discussed in Black A. P. et al., “Use of Iodine for disinfection”, J. Am. Water Works Assn., Vol. 57, 1965 and later variants of this design to the use of iodine complexes such as iodophors (Disinfection, Sterilization and Preservation, Fifth edition, Ed. Seymour S. Block, Chapter 8, “Iodine and Iodine Compounds”, W. Gottardi), and to dispersing iodine vapor through a barrier material. These mechanical or chemical approaches met with varying degrees of success and presented various restrictions in use. With respect to dissolving crystalline iodine in water, mechanical methods had problems with respect to particle carry-over and the use of iodine in admixture with other chemicals presented limitations on control of iodine concentration and introduced issues of contamination by other components of the formulation.
Vaichulis (U.S. Pat. No. 3,408,295) describes an apparatus and method for disinfecting or purifying water that relies on the flow of water to be treated through a bed of elemental iodine and the consequent formation of an iodine-containing solution. The aqueous solution passes through a porous body, such as a fritted glass disc, which has a porosity such that it is pervious to the passage of a water solution of iodine therethrough and impervious to the passage of iodine in undissolved form.
Polley (U.S. Pat. No. 4,384,960) shows that elemental iodine can be retained by several means inside a container and can be dissolved to form an aqueous iodine solution by expelling water from inside the container through the body of iodine. Only one of these means is claimed, being the placing of solid elemental iodine in a removable dropper tip of the container. Retention of solid iodine is provided for by materials that are porous or otherwise pervious to water but have perforations or openings therein sufficiently small to retain undissolved iodine.
Neither of these patents anticipates the practical use of the transfer of iodine vapor to produce aqueous iodine solutions nor do they adequately show how solid iodine is retained yet water flow is permitted.
The O'Dowd patent (U.S. Pat. No. 5,275,736) uses a non-porous, iodine-solving, solid barrier identified as a plastic material to enclose crystalline iodine which is permeable to diffusion of iodine vapor from the inside to the exterior medium where it can act as a disinfectant. The patent refers in particular to the use of Lugol's solution, tincture of iodine and an iodophor as the source of iodine. It was emphasized that these solutions contain a low percentage of available iodine. In addition, an iodophor, a complex of iodine, was selected to limit the rate of transfer of iodine. This method was intended to prevent the contamination of the exterior medium, provide for sustained replenishment of iodine in the exterior medium as it is consumed, and produce an aqueous iodine solution which is biocidal, yet without the physical disadvantages of common iodine-containing formulations. The patent identifies four plastic materials that can be used for the iodine-solving barrier: linear polyethylene, isotactic polyethylene, polyoxymethylene and polybutylene terephthalate. In practice, these permit only very low rates of transfer of iodine that are impractical for common use.
There are two explanations for this type of behavior. Firstly, the patent describes the rate and extent of transfer of iodine as being dependent on the relative vapor pressures of iodine on either side of the barrier as well as the physico-chemical nature of the barrier material. Over time, a balancing of these vapor pressures would take place such that the final concentration in the receiving medium would be directly related to the vapor pressure within the barrier. However, in reality, the rate of this vapor diffusion process is determined by the “Law of Mass Action” (Guldberg and Waage, 1864) with the rate of reaction dependent upon the molecular concentrations of the reactants, i.e. I2 and H2O, and the products. It is not surprising therefore that the observed rates of transfer are low and decline with time. Secondly, the examples of the solid barriers provided in this patent may be subject to poisoning which would reduce their effectiveness in use. Consequently, the process of iodine vapor transfer as described in the O'Dowd patent is exceedingly slow and is impractical for application to useful devices.
By contrast, the inventors of the methods, devices and uses of the current patent have focused on practical designs for generating iodine solutions. They use solid elemental iodine and other iodine compounds and have avoided the use of complexing agents such as are typical of iodophor formulations. In particular, they select porous, vapor-permeable membranes to enclose the iodine source and this combination has the distinct advantage of much higher transfer rates than the use of solid plastic materials described in the prior art.
The product of this invention, an essentially saturated aqueous solution of iodine, contains what is known as thermodynamically free iodine. This form of iodine is not complexed and is totally available chemically. According to Clough, (European Applied Research Reports: Nuclear Science and Technology, 1985, 6, 631, “A review of the aqueous chemistry and partitioning of inorganic iodine under LWR severe accident conditions”), elemental iodine (I2) reacts in aqueous solution to give numerous products in various proportions dependent on pH, temperature and iodine concentration. These include the dissociated, hydrolyzed forms of iodic acid (HI) and higher polyiodides, periodic acid (HOI), iodate (IO3−) and species such as OI−, HI2O2−, I2O2−and H2OI+. Of these, the major bactericidal species are I2 and its solvated species, I2.H2O and I2H.OH, HOI and iodine cation H2OI+ (which is only effective at a pH<1). Iodide (I−) (except that which is in hydrolysis equilibrium with HOI) and iodate (IO3−) are not germicidal. Highly diluted solutions (10−5 Mol/L or 2.54 mg/L) for potable or swimming pool water do not form iodates in the presence of iodide below a pH of 8.